Microcell electrochemical devices assemblies with water management subsystem, and method of making and using the same

ABSTRACT

A microcell assembly wherein water is generated by electrochemical reaction and sorptive channeling elements are provided in the assembly to remove excess water from the locus of electrochemical reaction. The water management techniques of the invention enhance electrochemical generation/conversion of energy, and facilitate high voltage, high power density outputs for applications such as fuel cell and battery systems.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to microcell electrochemical devices andassemblies, methods of making same by various techniques, and use ofsuch devices and assemblies.

2. Description of the Art

In the field of energy supplies and energy conversion devices, andparticularly in the development of fuel cells and batteries, there hasbeen continuing effort to develop devices with significant power outputs(high current and/or high voltage), high power density, and high energyoutput per unit volume.

Structurally, electrochemical cells such as batteries and fuel cells arerelatively simple, utilizing respective positive and negative electrodesseparated in such manner as to avoid internal short circuiting, and withthe electrodes being arranged in contact with an electrolyte medium. Bychemical reaction at the electrodes, the chemical energy of the reactionis converted into electrical energy with the flow of electrons providingpower when the electrode circuit is coupled with an external load.

Battery cells may use separator plates between respective electrodes sothat multiple sheet elements are arranged in successive face-to-faceassemblies, and/or such sheets may be wound together in a (spiral) rollconfiguration.

The fuel cell is of significant current interest as a source of powerfor electrically powered vehicles, as well in distributed powergeneration applications.

In fuel cells, a fuel is introduced to contact with an electrode (anode)and oxidant is contacted with the other electrode (cathode) to establisha flow of positive and negative ions and generate a flow of electronswhen an external load is coupled to the cell. The current output iscontrolled by a number of factors, including the catalyst (e.g.,platinum in the case of hydrogen fuel cells) that is impregnated in theelectrodes, as well as the kinetics of the particular fuel/oxidantelectrochemical reaction.

Currently, single cell voltages for most fuel cells are in the range ofabout 0.6-0.8 volts. The operating voltage depends on the current; ascurrent density increases, the voltage and cell efficiencycorrespondingly decline. At higher current densities, significantpotential energy is converted to heat, thereby reducing the electricalenergy of the cell.

Fuel cells also may be integrated with reformers, to provide anarrangement in which the reformer generates fuel such as hydrogen fromnatural gas, methanol or other feed stocks. The resulting fuel productfrom the reformer then is used in the fuel cell to generate electricalenergy.

Numerous types of fuel cells have been described in the art. Theseinclude:

polymer electrolyte fuel cells, in which the electrolyte is afluorinated sulfonic acid polymer or similar polymeric material;

alkaline fuel cells, using an electrolyte such as potassium hydroxide,in which the KOH electrolyte is retained in a matrix between electrodesincluding catalysts such as nickel, silver, metal oxide, spinel or noblemetal;

phosphoric acid fuel cells using concentrated phosphoric acid as theelectrolyte in high temperature operation;

molten salt fuel cells employing an electrolyte of alkali carbonates orsodium/potassium, in a ceramic matrix of lithium aluminate, operating attemperatures on the order of 600-700 degrees C., with the alkalielectrolyte forming a high conductive molten salt;

solid oxide fuel cells utilizing metal oxides such as yttria-stabilizedzirconia as the electrolyte and operating at high temperature tofacilitate ionic conduction of oxygen between a cobalt-zirconia ornickel-zirconia anode, and a strontium-doped lanthanum manganatecathode.

Fuel cells exhibit relatively high efficiency and produce only lowlevels of gaseous/solid emissions. As a result of these characteristics,there is great current interest in them as energy conversion devices.Conventional fuel cell plants have efficiencies typically in the rangeof 40-55 percent based on the lower heating value (LHV) of the fuel thatis used.

In addition to low environmental emissions, fuel cells operate atconstant temperature, and heat from the electrochemical reaction isavailable for cogeneration applications, to increase overall efficiency.The efficiency of a fuel cell is substantially size-independent, andfuel cell designs thus are scalable over a wide range of electricaloutputs, ranging from watts to megawatts.

A recent innovation in the electrochemical energy field is thedevelopment of microcells—small-sized electrochemical cells for battery,fuel cell and other electrochemical device applications. The microcelltechnology is described in U.S. Pat. Nos. 5,916,514; 5,928,808;5,989,300; and 6,004,691, all to Ray R. Eshraghi. The microcellstructure described in these patents comprises hollow fiber structureswith which electrochemical cell components are associated.

The aforementioned Eshraghi patents describe an electrochemical cellstructure in which the single cell is formed of a fiber containing anelectrode or active material thereof, a porous membrane separator,electrolyte and a second electrode or active material thereof. Celldesigns are described in the Eshraghi patents in which adjacent singlefibers are utilized, one containing an electrode or active materialthereof, the separator and electrolyte, with the second fiber comprisinga second electrode, whereby the adjacent fibers constitute positive andnegative electrodes of a cell.

The present invention embodies additional advances in the Eshraghimicrocell technology.

SUMMARY OF THE INVENTION

This invention relates to microcell electrochemical devices andassemblies, methods of making same by various techniques, and use ofsuch devices and assemblies.

The invention relates in one aspect to an electrochemical devicecomprising water-permeable membrane hollow fibers distributed in anassembly including a plurality of microcells potted at respective endsof the assembly and disposed within a housing wherein the pottedrespective ends bound an interior volume therebetween, and wherein thehollow fibers are parallely aligned with microcells of the assembly,with each hollow fiber having a first open end extending through thetubesheet exteriorly of the interior volume and the other endterminating at or before the opposite potting member, whereby the hollowfibers are arranged to absorb water produced in the electrochemicalreaction by wicking action and channeling water away from the locus ofelectrochemical reaction by permeation through the wall of the hollowfiber and flow thereof through the bore of the hollow fiber to acollection locus in the housing outside of the interior volume. Anotheraspect of the invention relates to an electrochemical cell module,comprising:

a multiplicity of microcells in an assembly comprising a multiplicity ofcomponent microcell sub-bundles,

each microcell comprising an inner electrode,

a microporous membrane separator in contact with the inner electrode,

an electrolyte in pores of the microporous membrane separator,

an outer electrode,

with the microcell assembly including a plurality of hollow fiber heatexchange elements arranged for flow of an aqueous coolant medium througha central lumen thereof, with the hollow fiber heat exchange elementsbeing distributed in the assembly for heat removal from the assemblyduring electrochemical reaction in operation of the module;

a source of the aqueous coolant medium;

flow circuitry interconnecting the source of said aqueous coolant mediumand said hollow fiber heat exchange elements;

wherein the hollow fiber heat exchange elements comprise awater-permeable porous membrane separator, whereby water deriving fromthe aqueous coolant medium permeates from the bore through the membraneseparator wall into the feed stream, thereby humidifying theelectrochemical reaction environment.

A still further aspect of the invention relates to a method of watermanagement in an electrochemical device including a plurality ofmicrocells potted at respective ends and disposed within a housingwherein the potted respective ends bound an interior volumetherebetween, such method comprising arranging hollow fibers to absorbwater produced in the electrochemical reaction by wicking action,channeling water away from the locus of electrochemical reaction bypermeation through the wall of the hollow fiber and flowing same throughthe bore of the hollow fiber to a collection locus in the housingoutside of the interior volume.

Another aspect of the invention relates to a method of making anelectrochemical cell module, comprising:

a multiplicity of microcells in an assembly comprising a multiplicity ofcomponent microcell sub-bundles,

each microcell comprising an inner electrode,

a microporous membrane separator in contact with the inner electrode,

an electrolyte in pores of the microporous membrane separator,

an outer electrode,

comprising fabricating the microcell assembly with a plurality of hollowfiber heat exchange elements arranged for flow of an aqueous coolantmedium through a central lumen thereof, with the hollow fiber heatexchange elements being distributed in the assembly for heat removalfrom the assembly during electrochemical reaction in operation of themodule;

wherein the hollow fiber heat exchange elements comprise awater-permeable porous membrane separator, whereby water deriving fromthe aqueous coolant medium permeates from the bore through the membraneseparator wall into the feed stream, thereby humidifying theelectrochemical reaction environment.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are perspective views of fibrous element structuresillustrating the fabrication of a microcell assembly.

FIG. 5 is a perspective view of a connector for joining currentcollector or electrode elements of a microcell fiber assembly.

FIG. 6 is a microcell assembly according to one embodiment of theinvention, with a terminal at one end of the assembly.

FIG. 7 is an exploded perspective view of a microcell assembly showingseries-connected microcell sheets.

FIG. 8 is a schematic view of a layered arrangement of microcell sheets,joined in series relationship.

FIG. 9 is a 3-dimensional perspective view of a series-connectedarrangement of microcell layers.

FIG. 10 shows a potted arrangement of microcell sheets.

FIG. 11 is a perspective view of a duct that is perforated on the topsurface, and optionally on the bottom surface for the fabrication ofdouble stack bundles of electrochemical cells.

FIG. 12 is a cross-sectional elevation view of a microcell fiber bundlepotted in a vessel.

FIG. 13 is a side elevation view of the vessel of FIG. 12.

FIG. 14 is an elevational cross-sectional view of a double stack ofmicrocell sheets.

FIG. 15 is a side elevation view of a double stack of microcell devicesarranged in sheets, comprising a stack on each side of a perforatedduct.

FIG. 16 is a perspective view of potted fibers on one side of aperforated feed duct.

FIG. 17 shows a vessel with fibers laid on both sides of the perforatedfeed duct.

FIG. 18 is a side elevation view of an electrochemical cell devicecomprising an assembly of microcells.

FIG. 19 shows a perforated feed tube used as a mandrel in formingmicrocell structures.

FIG. 20 shows fibrous microcell and shell side current collector sheetsthat can be rolled or wound around the perforated tube of FIG. 19, withthe sheets being shown during rolling in FIG. 21 and as finally rolledinto shape in FIG. 22.

FIG. 23 shows sheets of fibrous microcell elements and shell sidecurrent collectors, and an insulating sheet (e.g., of fiberglass orporous plastic material).

FIG. 24 is a perspective view of a sheet assembly including two sheetsof fibrous microcell elements and shell side current collectors.

FIG. 25 is a side elevation view of a microcell assembly with off-setfiber layer sheets.

FIG. 26 is a cross-sectional view of a microcell bundle.

FIG. 27 is a side elevation view of series-connected microcellsub-bundles according to one embodiment of the invention.

FIG. 28 is a perspective view of a connector that may be used to joincomponent microcell sub-bundles in series.

FIG. 29 is a cross-sectional elevation view of a multibundle assembly,wherein each bundle has a corresponding feed tube associated therewith.

FIG. 30 is a cross-sectional elevation view of a multibundle assembly,wherein the respective bundles are connected in series.

FIG. 31 is a cross-sectional view of a fuel cell module with multiplesub-bundles wherein blank seal elements provide closure members for theface sheet of the module enclosure.

FIG. 32 is a side view of a fuel cell module with multiple sub-bundlesof microcell elements, with a feed tube in a manifolded arrangement.

FIG. 33 is a side elevation view in section, showing penetration of afeed tube into the interior volume of the housing of a module containingmicrocell sub-bundles according to one embodiment of the presentinvention.

FIG. 34 is a cross-sectional view of a microcell assembly in which heatexchange fibers or tubes are provided in interspersed relationship tothe microcell bundles.

FIG. 35 is a cross-sectional elevation view of a fuel cell module,showing air/fuel passages and heat exchange passages, interspersedbetween the sub-bundles.

FIG. 36 is a cross-sectional view of a microcell bundle wherein hollowfibers function as outer electrode elements and enable heat exchange.

FIG. 37 is a side elevation in cross section of a fuel cell with heatexchange/current collector hollow fibers.

FIG. 38 is a cross-sectional elevation view of a fuel cell module withheat exchange from current collectors by means of conduction.

FIG. 39 is a schematic depiction of a fuel cell system, according to oneembodiment of the invention.

FIG. 40 is a cross-sectional view of a double membrane design with anelectrically conductive perm-selective membrane on the anode or cathodeelement of the microcell.

FIG. 41 is a cross-sectional view of a double separator design withperm-selective membranes protecting the anode or cathode elements of themicrocell.

FIG. 42 is a cross-sectional view of a double separator design withperm-selective membranes covering both anode and cathode elements of themicrocell.

FIG. 43 is a cross-sectional view of a double separator design withperm-selective membranes covering both anode and cathode elements of themicrocell and with a porous, electrically conductive inner separator.

FIG. 44 is a cross-sectional view of a double separator design withperm-selective membranes covering both anode and cathode elements of themicrocell and with reformer catalyst on the inner wall of the innerseparator.

FIG. 45 is a schematic flowsheet of a solution impregnation system forimpregnation of a membrane fiber with Nafion or electrocatalyst.

FIG. 46 is an elevation view of a metallic fiber having a polymericcompound on its outer surface.

FIG. 47 shows the corresponding fiber of FIG. 46 after pyrolysis, with apyrolyzed carbon coating on the outside surface thereof.

FIG. 48 shows a fibrous carbon current collector laid along a coatedmetallic fiber.

FIG. 49 shows the fiber assembly of FIG. 48 after a disconnection breakof the coated metallic fiber.

FIG. 50 shows a cross-section of a hollow fiber and microcell tubebundle, in which the plane hollow fiber elements are used for channelingwater from the assembly.

FIG. 51 shows a vertically upward extending bundle of microcells,arranged so that water from the module drains to a lower plenum spacefor removal.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

The disclosures of Eshraghi U.S. Pat. Nos. 5,916,514; 5,928,808;5,989,300; and 6,004,691 hereby are incorporated herein by reference, intheir respective entireties.

As used herein, the term microcell refers to an electrochemical cellenergy generation or conversion structure, including a porous membraneseparator having electrolyte disposed in porosity thereof. The porousmembrane separator is in contact with electrically conductive fibersthat in turn are in contact with or are coated with electrocatalystforming positive and negative electrodes for the electrochemical cell.

While the ensuing description herein is primarily directed to fuel cellembodiments of the instant invention, it will be appreciated that thedescription can be analogously applied to corresponding battery cellsand to other forms of electrochemical cell devices, consistent with theinvention.

A battery cell of course differs from a fuel cell in that the(electrode) active material in a battery is present and stored in thecell, as opposed to being externally furnished to the structure whenelectrochemical activity is desired.

Accordingly, when used in a battery cell, the microcell does not requirea lumen at the center of the fiber, thereby correspondingly simplifyingthe bundling of fibers in modular assemblies for battery cellapplications. Microcells for battery cell applications thus havestructural and operational differences from microcells used in fuelcells.

In a specific form, the microcell comprises an inner electrode activematerial, a microporous membrane separator in contact with the innerelectrode active element, electrolyte in pores of the microporousmembrane separator, and an outer electrode active element, wherein eachof the inner and outer electrode active elements comprises at least oneof electrode, current collector and electrocatalyst components.

In another specific form, the microcell may include a fibrous, innerelectrode that is encapsulated by a microporous membrane separator withan electrolyte disposed in porosity of the microporous membraneseparator, and with electrocatalyst impregnated or coated on the bore orshell side of the fiber (to form an inner or outer electrode,respectively) along with electrically conductive material.

In fuel cell applications, the bore of the microcell hollow fiberdefines a lumen for passage therethrough of gaseous or liquid feed(e.g., fuel or oxidant) components. A wide variety of electrolyte typescan be used in the microcell fuel cell, depending on the specificapplication involved.

In a preferred form, all components of the microcell are fabricated in asingle fiber assembly. The microcells can be of any predeterminedlength, typically with a length to diameter ratio significantly greaterthan 1, and are readily formed into microcell assemblies, includingbundled forms as hereinafter described in greater detail. Such microcellassemblies, or collections of such assemblies, may be aggregated to forma fuel cell module, similar in overall arrangement to a shell and tubeheat exchanger.

When the microcell elements are fabricated into bundled multi-cellmodules in a unitary overall construction, the resulting compact unitaryconfiguration provides high density energy output and enablesminimization of the volume (and “footprint”) of the fuel cell or otherelectrochemical cell apparatus fabricated from such bundles.

The microcell apparatus of the invention in one embodiment is fabricatedwith the inner electrode (or a multiplicity of current collector fibers)being encapsulated by a microporous membrane separator. Theelectrocatalyst of the inner electrode in such embodiment is coated orimpregnated on the inner wall of the membrane separator (or coated onthe inner current collector fibers).

The electrocatalyst in one embodiment is impregnated onto the membraneseparator wall from a catalyst solution. In another, alternativeembodiment, a thin ink formulation of the catalyst is pumped through thebore of the membrane separator during the membrane spinning process.

One technique of forming porous separator membrane-electrode assembliesinvolves coating current collector fibers with an electrocatalystformulation. Such coating in one embodiment is carried out in anextrusion process. In another embodiment, the current collector fibersare coated from a plating solution. In yet another embodiment, thecurrent collector fibers are coated by plasma deposition of a metalcatalyst.

In forming a fuel cell stack or module, the microcell fibers are bundledand potted in order to isolate and seal the bore side and the shell sideof the cells. For large fuel cell structures, microcells may be bundledaround a perforated mandrel, such that the mandrel becomes the gas inputstructure for the shell side of the cells.

With respect to the microporous membrane separator element as used infuel cell embodiments and in other electrochemical cell embodiments ofthe present invention, any suitable means and method for electrolyteimpregnation or incorporation are usefully employed. An illustrative andpreferred technique for impregnation of the electrolyte is solutionimpregnation.

The porous membrane separator element itself can be of widely varyingtype and structure, and formed for a specific type of fuel cell or otherelectrochemical cell application. For polymer electrolyte fuel cells,for example, an asymmetric channelized porous structure is preferred toprovide a contiguous phase of the ion exchange polymer adjacent to theelectrocatalyst layer. For acid or alkaline fuel cells, a foam-likestructure of the porous membrane element is desirable. The choice ofmembrane separator conformation and morphology is readily determinablewithout undue experimentation, as will be appreciated by those skilledin the art.

Fuel cells formed from microcells in accordance with a preferred aspectof the invention are monopolar and do not require bipolar flow fieldplates. Since the cells and current collectors are in fiber form, a highlevel of electrode surface area can be compacted in very small volumes.In parallel connection of individual bundled cells, wherein current isadditive, very high current density per unit volume is achievable,allowing the microcell assembly to operate at high voltage and highefficiency.

In one embodiment, inner electrodes of respective microcells areconnected to form a first terminal of a microcell assembly, and currentcollectors on the outer shell of the fiber elements or on the outershell of a bundle of such microcells, forms a second terminal. When suchassembly is constructed and arranged for fuel cell usage, fuel andoxidant are passed over electrodes on the corresponding respective shelland bore sides of the bundle. In the individual microcell elements ofthis fuel cell, the microporous membrane is impregnated with anappropriate electrolyte and forms a barrier or separator element.Depending on the electrolyte type, the microporous matrix andelectrolyte can combine to form a new structure in the form of a solidmatrix or a liquid-solid matrix.

In fuel cell applications utilizing microcell devices containing asingle fiber inner electrode element, the size of the inner electrodeelement is selected to provide an appropriately dimensioned lumen on thebore side of the membrane separator containing the electrode. Multiplefibers can also be positioned in the bore of a hollow fiber membraneseparator to provide interstitial space forming a lumen in the hollowfiber. The formation of the lumen is important since the lumen allows(liquid or gaseous) fuel or oxidant to reach the inner electrode in theoperation of the fuel cell.

In a preferred form, an electrocatalyst and the electrically conductivematerial of a second electrode is coated, extruded or impregnated on theouter shell of the microporous membrane separator and electrolyte isdisposed in the micropores of the membrane separator, to complete themicrocell structure.

The microporous membrane separator may be formed of any suitablematerial of construction. In one embodiment, the microporous membraneseparator is fabricated from a material selected from the groupconsisting of semi-permeable, ion-exchange membranes, and a porousmembrane coated on a shell or bore side thereof with a perm-selective oran ion-exchange polymer.

In the microcell structure, the inner electrode or current collector isretained in a tightly-held manner in the bore of the separator and iscontiguous to the inner wall of the fiber, for interfacial contact withthe electrolyte or electrolyte/electrocatalyst layer. The outerelectrode or current collector also makes intimate contact with theshell side electrolyte, or with the electrolyte/electrocatalyst layer ofadjacent cells, when the fibrous microcell structures are denselybundled with one another.

Accordingly, the lumen of the microcell structure in fuel cellapplications must be sufficiently “open” to allow passage of the gaseousfeed (fuel or oxidant) through the lumen during normal operation. Forsuch purpose, the fuel cell apparatus desirably includes a pump, fan,blower, compressor, eductor, or the like. Since the flow rates requiredfor fuel cell operation entail relatively low pressure differentials,pumping requirements (for gaseous feed flow through the lumen of themicrocell hollow fiber) are readily accommodated by commerciallyavailable fluid driver devices of the above-mentioned types.

Series Connection of Microcell Structures and Assemblies

To achieve high current density at a single microcell voltage level, anumber of microcells are connected together in parallel. Parallelconnection of microcells for such purpose is readily effected bybundling the microcells in parallel relationship to one another andconnecting the end portions of the current collectors at each extremityof the resulting microcell assembly.

In order to achieve high voltages, however, above the voltage affordedby a single microcell, it is necessary to connect microcells in serieswith one another. As described more fully hereinafter, various methodsmay be employed to effect series connection, depending on the geometryof the microcell assembly that is desired. For example, a rectangularconfiguration or a cylindrical configuration may be desired.

In accordance with the invention, a sub-bundle of parallel fibrousmicrocells is first constructed to obtain the desired current. Thesub-bundles then are connected in series to achieve a desired voltage.

One preferred approach to forming a sub-bundle microcell assembly is toform a sheet arrangement of generally parallelly aligned microcellelements, wherein the microcells are in side-by-side relationship to oneanother, with the current collectors extending from one end of thegenerally planer sheet, in side-by-side register with one another (i.e.,so that the current collector ends are generally arranged in a singleplane with respect to one another, or otherwise so that the currentcollectors protruding from the microcells are generally coextensive inlength relative to the face of the microcell sheet assembly from whichthey protrude). Next, the first layer of microcell elements is overlaidby a second layer comprising outer current collector elements, arrangedso that the outer current collectors extend from an opposite side of thesuperimposed sheet from that from which the inner current collectorsprotrude. The outer current collectors likewise extend outwardly to agenerally same length, so that the ends of the outer current collectorsare in register with one another, residing generally in a singlevertical plane relative to a flat, horizontal plane of the sheetassembly.

For purpose of forming the above-described sheet assembly, theconstituent fibrous microcell elements in the first layer may be securedto one another to provide a unitary web or sheet form of such elements.In like manner, the outer current collectors overlaid on the fibrousmicrocell elements may be secured to one another to a sheet or webconfirmation, such as by an inner connecting mesh or woven structure,transversely laid strips of adhesive tape, or other means by which aparallel assembly of current collector elements is provided.

It will be appreciated that any suitable means and methods may beemployed to form the respective sheet-like layers of the microcellassembly just described. Such layers can be pre-formed, for example, byweaving the microcell or current collector fibers into sheets orembedding them in a resinous matrix, or in any other suitable manner.

Once the layer of microcell elements and the layer of outer currentcollector elements is contacted in superimposed relationship with oneanother, the composite structure then can be rolled into a cylindricalshape and potted at each of respective opposite ends, to form asub-bundle assembly comprising a multiplicity of microcells.

Potting of such assembly can be carried out in any suitable manner,using methods conventionally employed to pot hollow fiber membranes,e.g., in the fabrication of hollow fiber filtration modules. Eachresultant potted sub-bundle thereby has a positive and negative terminalat each end, with one such terminal being formed by the inner currentcollector elements protruding from the microcell elements of thefirst-described layer, and the other terminal being formed by the outercurrent collector elements protruding from the opposite end of thesub-bundle.

Sub-bundles then are connected in series by connecting the positiveterminal of a first sub-bundle to a negative terminal of a nextsub-bundle, and so on in consecutive fashion. The resulting long strandof connected sub-bundles then is re-bundled into a cylindrical shape, byfolding each bundle in an alternating fashion at each end and at theconnection between each succeeding microcell. The resulting assembly ofsub-bundles folded into parallel arrangement with one another then ispotted again at each end thereof to form a bundle as a compositestructure comprising a multiplicity of sub-bundles.

The bundle in consequence contains fibrous microcells in both paralleland series connection, constituted in a unitary structure that may thenbe placed in a casing in the manner of a shell and tube heat exchangeassembly, as hereinafter described in greater detail.

It is evident from the foregoing discussion that the avoidance ofshort-circuiting between sub-bundles requires that each sub-bundle becovered or encased with a porous yet electrically insulating material.Accordingly, each sub-bundle may be sheathed or sleeved in a fiberglassor polymeric material encasement member, in to which the sub-bundle maybe inserted or about which the encasement material may be wrapped.

Sub-bundles alternatively may be formed and the packed into a bundle byalternating each end so that a positive terminal end of a sub-bundle isin proximity to a negative terminal of another sub-bundle. Thesub-bundles in this alternative technique can first be potted and thenconnected in series, by connection of the positive terminal of a firstsub-bundle to a negative terminal of a next adjacent sub-bundle. Thesub-bundles may be connected simply be making an electrical connectionbetween each microcell. Alternatively, an end plate having a mirrorimage of the location of sub-bundle connection nodes (where all themicrocell fibers are connected in parallel in a sub-bundle) on its face,and an imprint of series connections of the terminals designed and builtinto the plate may be employed, so that electrical connection of theplate with each node of the bundle will automatically yield a seriesconnection.

As yet another alternative to sub-bundle potting, each sub-bundle may befabricated with a sealed tube sheet member at each end. Each sub-bundlethen can be inserted into a casing having openings at each end thereofthat are the same size as the parameter (outer circumference) of thesub-bundle. In such fabrication, each sub-bundle may be sealed at eachrespective end of the housing, e.g., with O-ring seals or other sealingmeans, without the requirement of having to pot the sub-bundles again.In such configuration, each sub-bundle can be removed from or introducedto the housing in a simple and readily affected manner, allowing forincrease or reduction in power generation capacity of the overallmicrocell apparatus.

Alternatively, a sub-bundle article can be fabricated in a rectangularconfirmation by placing layers of microcells and outer currentcollectors over each other in alternating and repeating sequence toachieve a desired height and rectangular cross-section. The constituentlayers of microcell fibrous elements and outer current collectors can bepreformed in sheet-like form, as previously described.

In forming a series connection of sub-layers of respective fibrousmicrocell elements and outer current collectors in the respectivelayers, the current collector elements are generally of similar lengthcharacteristics to the fibrous microcell elements, such that respectivefibrous microcell element and outer current collector layers arelongitudinally off-set in relation to one another. In such arrangement,the outer current collector elements are longitudinally displaced beyondone end of the fibrous microcell element layer, and is correspondinglyshorter at the opposite end so that the first layer (underlying layer)of fibrous microcell elements extends beyond the ends of the layer ofouter current collectors.

Thus, at each end of the layered assembly, there is a line of “shortends” of the upper or lower layer, and it is at this short end that thepotting member is formed at each of the ends of the overall assembly.

On this sub-layer assembly a layer of porous, electrically insulatingsheet material is placed, and a second sub-layer assembly then is formedon the porous, electrically insulating sheet. In the second sub-layerassembly, a bottom layer is placed directly on the porous, electricallyinsulating sheet and overlaid with a layer of outer current collectors,off-set from one another, and arranged such that the positive terminalof the new sub-layer is on the same side of the overall assembly as thenegative terminal of the first sub-layer. This pattern of fabrication iscontinued until a desired sub-layer height is reached and a desiredvoltage is achieved. The ends of the respective positive and negativecurrent collectors from each end are then connected to each other with,for example, an electrically conductive rod or strip member, ashereinafter described.

Alternatively, the layered assembly may be fabricated, with electricalconnection of the fiber sheets with positive and negative ends fromadjoining sub-layers initially, prior to stacking of the respectivesub-layers. A final stack of sub-layers is then potted at both ends ofthe assembly, to isolate and seal the bore of the sub-layer assemblyfrom the shell side. The potted bundle of the fiber stack then can beplaced on a perforated duct that will function as a feed inlet to theshell side of the hollow fibers in the assembly. The fibrous microcellelements and the outer current collectors can alternatively be potted asthe fibers are being layered, e.g., by depositing a line or bead ofepoxy or other potting compound at both ends as the respective layersare being laid. The viscosity of the potting material is suitably chosenso that complete wetting of the fibrous microcell elements takes place,to ensure leak-tightness of the resultant tube sheet.

Once potted, the bundle or stack of microcell layers is placed in ahousing such that the shell and bore of the microcell elements aresealed and isolated when a feed is introduced on either side (shell sideor bore side). The resulting unit has the confirmation of a rectangularshell and tube heat exchanger, and such unit is advantageouslyfabricated with at least one inlet to the housing for introducing feedto the bore side and at least one outlet in the housing for removingdepleted feed from the bore side.

When the microcell elements are provided in a stack of layers, suchstack is placed on a duct perforated between the potting members atrespective ends. A non-perforated section of the duct extends throughone end of the housing, e.g., with the feed inlet or outlet on the boreside of the microcell elements, as described, and with the ductextending sealingly through the housing to provide a feed inlet to theshell side of the microcell elements. The layered microcell stacks maybe placed on both sides of a perforated feed duct to form a symmetricdouble stack, as hereinafter described in greater detail.

In accordance with one aspect of the present invention, smallsub-bundles of microcell assemblies can be electrically connected inseries in the same cell housing, or smaller fuel cell modules can beelectrically connected in series to increase the overall cell voltage.One approach for achieving high voltage levels, in accordance withanother embodiment of the present invention, is to manifold fuel cellstacks (each comprising a plurality of microcell devices) to gas feedsin a parallel fashion, with the stacks themselves being series-connectedassemblies of microcell bundles.

In one embodiment, electrically conductive fibers are bundled withmicrocell devices, so that the electrically conductive fibers functionas current collectors on the shell side of the fibers. The shell sidecurrent collectors, or alternatively the outer electrodes coated withsuitable electrocatalyst, are connected to a common plate to constitutea first terminal for the bundled assembly. Correspondingly, innerelectrodes extending through the bore of the microcell fibers areconnected to a plate forming a second terminal for the assembly.

In such fuel cell assembly, fuel or oxidant is passed over theelectrodes on the corresponding respective bore or shell side of thefibers, and the electrolyte-incorporating membrane separator preventsmigration of the fuel or oxidant to the other electrode.

In accordance with the invention, the microcell fiber structures areusefully potted to form sub-bundles of a larger ultimate bundledstructure, with the sub-bundles being connected in series or parallel(or, as discussed hereinafter, some structures or sub-bundles can beparallel connected, with the parallel-connected assembly of microcellelements then being series-connected to other sub-bundles; the conversearrangement, wherein series-connected microcell elements formsub-bundles that are parallel-connected to one another, also is usefullyemployed in some applications).

In one preferred embodiment, sub-bundles of the microcell fiberstructures are fabricated, and then the sub-bundles are aggregated withother sub-bundles, and potted again to form the fuel cell module. Thepotting medium advantageously used for such structural fixation of themicrocell fiber structures or sub-bundles is any suitable potting orencapsulant medium, such as epoxy, urethane, silicone, EPDM rubber, orother encapsulant media.

The sub-bundles can be made with tube sheets at each end with O-ringseals, similar to the process employed in the final module assembly, andwith the sub-bundles then inserted in a metal or polymeric sheetmaterial having holes formed in it. The fuel cell casing then will havetwo faces, one at each end, with holes cut into it the size of the outerdiameter of the sub-bundled tube sheet.

By this arrangement, sub-bundles can be added to or removed from theoverall module to increase or decrease power (e.g., in a power sourcefor stationary application, or alternatively for motive transportapplications such as electrical vehicles, to provide adjustable vehiclepower). The holes in the faces can be sealed with blank sheets of thesame size as the holes, if sub-bundles are removed from the module. Thisfeature also provides capability for servicing individual sub-bundles,by removing defective sub-bundles and replacing them with newsub-bundles. The sub-bundles can themselves be potted units comprisingsmaller sub-bundles.

FIGS. 1-4 are perspective views of fibrous element structuresillustrating the fabrication of a microcell assembly.

As shown in FIG. 1, a fibrous microcell element sheet 10 is formed of aplurality of fibrous microcell elements 12, laid side by side oneanother in parallel alignment. The respective fibrous. microcellelements 12 can be consolidated by a plurality of sewn seams 16 asshown, or by use of tape, adhesive bonding or other method of affixationto produce a unitary fibrous microcell element sheet.

The sheet 10 as illustrated is aligned with first ends 18 of theelements 12 being in transverse register with one another, i.e., theends are generally coextensive in axial extent with one another, so thatthe ends 18 lie in a common vertical plane extending across the face ofthe sheet from which the internal current collectors 14 protrude.

In like manner, the opposite ends 20 of the fibrous microcell elements12 are in transverse register with one another, with the ends generallyaligned with one another in a transversely extending vertical plane atthe opposite face of the fibrous microcell elements 12.

In this manner, the fibers are laid flat adjacent to one another andconsolidated in a web structure, to form a sheet of fibers.

A plurality of external current collectors 24 are likewise securedtogether in parallelly aligned side by side arrangement, by a sewn seam26, or alternatively, a tape, glue strip, or other consolidating means,to form a sheet 22 as shown in FIG. 2. In such sheet 22, the respectiveends 28 and 30 of the constituent current collectors 24 are in registerwith one another so that all ends of the fibrous current collectors ateach extremity of the web lie in a transversely extending vertical planeat such extremity.

Next, the sheet 10 of fibrous microcell elements 12 and the sheet 22 offibrous current collector elements 24 are stacked, with the currentcollector sheet 22 on top of the fibrous microcell elements sheet 10, toform a conjoint structure 32 as shown in FIG. 3.

In such conjoint structure 32, the respective sheets 10 and 22 arelongitudinally off-set with respect to one another, so that the internalcurrent collector elements 14 of sheet 10 extend beyond the ends of theexternal current collectors of sheet 22 as shown, and with the externalcurrent collectors of sheet 22 correspondingly extending beyond the endsof the internal current collectors 14 of sheet 10 at the opposite end ofthe conjoint structure. The respective external current collectors ofthe overlying sheet 22 thus are in contact with associated fibrousmicrocell elements in the underlying sheet 10.

In FIG. 4, the conjoint structure 32 of FIG. 3 is a bottom layer of anassembly that is formed by overlying the bottom layer with a secondlayer 36 including a parallely aligned arrangement of fibrous microcellelements 38 forming a corresponding sheet, and overlaid in the secondlayer by a sheet including external current collectors 48 securedtogether by a sewn seam 40 as shown.

In the second layer, the fibrous microcell elements 38 are in registerwith one another at their respective ends 42 and 44, and the sheet ofexternal current collectors 48 is longitudinally displaced from thesheet of fibrous microcell elements 38. By such arrangement, theexternal current collectors 48 extend beyond the ends 42 of the fibrousmicrocell elements 38, and the internal current collectors 46 of thefibrous microcell elements 38 extend beyond the ends of the externalcurrent collectors 48.

Concurrently, the longitudinally protruding current collectors from therespective first and second layers at each of the ends of the assemblyare coextensive in axial extent with one another. A porous insulatinglayer of polymeric or fiberglass sheet 50 is placed between the layers32 and 36, as shown in FIG. 4.

FIG. 5 is a perspective view of a connector 52 for joining currentcollector or electrode elements of a microcell fiber assembly. Theconnector 52 has two leaves 54 and 56 that are at a 90° angle inrelation to one another, with the leaves being crimpable toward oneanother. When a group of current collector or electrode elements isplaced between the leaves of the connector and the leaves are crimpedtogether, the current collector or electrode elements then are securedin electrical contact with one another.

FIG. 6 shows the microcell assembly of FIG. 4, with the currentcollector elements at the right-hand portion of the drawing shown asbeing secured to the connector 52 so that the current collector elementsare coupled in electrical contact with one another.

FIG. 7 is an exploded perspective view of a microcell assembly 70showing series connected microcell sheet layers 60, 62, 64 and 66. Thebottom sheet layer 60 comprises internal current collector elements thatare connected by connector 72, and the overlying sheet of externalcurrent collectors in such layer are in turn joined to connector 74.

The next upper layer in the assembly includes internal currentcollectors connected by connector 78, which is joined by interconnect 76to connector 74, as well as external current collectors joined toconnector 80.

Connector 80 is joined by interconnect 82 to connector 84 of the nextupper layer in the assembly. Connector 84 connects the internal currentcollectors of such next upper layer, and the connector 86 at theopposite end of the layer connects external current collectors of thelayer to the connector 90 of the top layer in the assembly viainterconnect 88.

Connector 90 connects the internal current collectors of the top layerin the assembly and the external current collectors at the opposite endof the top layer of the assembly are connected by connector 92.

Each of the constituent layers in the assembly is separated from anadjacent layer by a corresponding porous insulative sheet 94, 96 and 98,respectively.

By the foregoing arrangement, each of the constituent layers in theassembly of FIG. 7 is joined to a next adjacent layer in head-to-tailseries relationship, as is evident from the indicated polarity of therespective connectors in the drawing.

FIG. 8 is a schematic view of an assembly 100 comprising a layeredarrangement of microcell layers joined in series relationship, includinglayers 102 and 104, separated by porous insulating sheet 110, layers 104and 106, separated by porous insulating sheet 112, and 106 and 108,separated by porous insulating sheet 114.

FIG. 9 is a three-dimensional perspective view of a series-connectedarrangement 130 of microcell layers. The lowermost layer is illustrativeand comprises a sheet of fibrous microcell elements 122 from whichinternal current collector elements 124 protrude at the left-hand sideof the layer, with overlying sheet of external current collectorelements 126 completing the microcell layer. The lowermost layer isshown as being electrically segregated from the next upper layer by aporous insulating layer 128, as schematically illustrated. The otherlayers are analogously constructed. The uppermost layer 130 as showncomprises three fibrous microcell elements arranged in side-by-siderelationship, and the other sheets of fibrous microcell elements in theassembly are correspondingly constituted. In this manner, a bundledmicrocell structure is formed.

FIG. 10 shows a potted arrangement 136 of microcell sub-bundles 138, inwhich component sub-bundles are connected by series connection of theirrespective opposite current collector elements 140 and 142, whereinadjacent sub-bundles are separated from electrical contact and potentialshort-circuiting by porous, insulative sheet 147. As shown, thesub-bundles 138 are potted at their respective ends by potting members144 and 146.

FIG. 11 is a perspective view of a duct 150 that is perforated withopenings 154 on the top surface 152, and optionally on the bottomsurface (not shown in the view of FIG. 11) for double stack bundles ofthe microcell layers. Two retaining walls 156, 158 are on each side, toretain the fiber sheets in position. Fibers are stacked on top of eachother on the perforated duct until the desired voltage is achieved. Afluid ingress/egress conduit 160 is joined to the interior plenumchamber of the duct 150, as shown.

Fiber sheets can be potted with epoxy as they are laid. Alternatively,the fiber sheets can be bundled and potted in the vessel to finish theprocedure. Fibers are potted at each end such that the open end remainsopen. The perforated duct will be the feed port to the shell side of thefibers.

FIG. 12 shows a cross-sectional elevation view of a fiber bundle 162potted in a vessel 150. The fiber bundle comprises layers 164 and 166 offibrous microcell elements, with an interposed sheet 168 of externalcurrent collector elements and with a separator sheet 170 of porousinsulative material between adjacent current collector and fibrousmicrocell element sheets. The bundle is potted by potting member 163.

FIG. 13 is a side elevation view of the vessel of FIG. 12, showing theretaining wall 156, and fluid ingress/egress conduit 160 of the housing,as well as the terminal connections at the respective faces 180 and 182of the bundle.

FIG. 14 shows a potted arrangement 186 of fibrous microcell elementsheets, in two sub-bundles 188 and 190 on opposite sides of feed duct196 receiving feed gas via inlet 198. The feed duct has perforations onboth top and bottom surfaces, and each of the constituent sub-bundles ispotted with the top sub-bundle being potted by potting member 192 andthe bottom sub-bundle being potted by potting member 194.

FIG. 15 shows a side elevation view of a double stack arrangement 200,comprising a stack of microcell elements on either side of theperforated duct. The gas feed 198 is shown in the drawing. Thearrangement shown in this drawing includes connector/terminal elements202, 204 and 206 connecting the corresponding current collectorelements.

FIG. 16 is a perspective view of an assembly 210 of potted fibrousmicrocell elements on one side of a perforated feed duct including gasinlet 224 and retaining wall 216. The potted rectangular bundle ofmicrofibers is arranged with its respective ends potted by pottingmembers 218 and 220.

FIG. 17 shows a corresponding vessel 230 when fibers are laid on bothsides of the perforated feed duct 238. The vessel comprises a centralsection 232 with an outlet 242 for discharging gas from the shell sideof the microcell assembly, end section 234 featuring outlet 248 forexhausting bore-side spent gas and end section 236 with inlet 246 forintroducing bore-side gas into the housing. The perforated feed duct isarranged to introduce feed gas into the central section 232 of thehousing for flow on the shell side thereof.

FIG. 18 is a sectional elevation view of system 250 including amicrocell bundle 280 potted at respective ends thereof by pottingmembers 266 and 268, which are leak-tightly secured to the inner surfaceof the housing 252 by O-ring elements 270 and 272.

The housing 252 has a flange element 256 joining the end section 258 ofthe housing with the central section. The central section of the housingcontains interior volume 252, which is separated from end volume 278 bypotting member 268 and from end volume 282 by potting member 266. Feedinlet 276 communicates with end volume 278 and end volume 282communicates with spent gas outlet 284.

Spent gas outlet 264 communicates with the interior volume 262. Feedtube 260 extends into the center of the microcell bundle 280 in theinterior volume 262, and is perforate along its length to introduce feedgas to the shell side of the microcell bundle 280 in the interiorvolume, with the spent gas being discharged in outlet 264. Feedintroduced into end volume 278 from inlet 276 flows through the boreside of the microcell elements in the bundle 280, and flows out of thebundle into end volume 282, following which it is discharged from thehousing 252 in outlet 284.

The current collectors are joined to terminal 292 in the end volume 282,with the terminal structure extending exteriorly of the housing 252. Atthe opposite end volume 278, the other ones of the inner and outercurrent collectors are joined to terminal 290, which extends exteriorlyof the housing.

FIG. 19 shows a perforated feed tube 300 with open ends 302, havingperforations 308 along a central part 306 of its length.

FIG. 20 shows fibrous microcell and shell side current collector sheets312, 314 that can be rolled or wound around the perforated tube 300 ofFIG. 19, with the sheets being shown during rolling in FIG. 21 and asfinally rolled into shape in FIG. 22.

The sheets will be placed on top of each other such that the ends of thefibrous microcell sheet 312 extend farther than the shell side currentcollector sheet 314 on one side, and the shell side current collectorsheet 314 extends farther on the other side. The sheets 312, 314 thenare wrapped tightly around the perforated tube 300 and then potted bypotting members 322 and 324.

FIG. 23 shows sheets 332, 334 of fibrous microcells and shell sidecurrent collectors, and an insulating sheet 330 (e.g., of fiberglass orporous plastic material). FIG. 24 is a perspective view of a sheetassembly 338, 340, 342, 344 and 346, including two sheets of fibrousmicrocells and shell side current collectors.

FIG. 25 is a side elevation view of a microcell assembly 338, 340, 342,344 and 346 with off-set fiber layers. The electrically insulating sheetis placed between two layers of fibers forming a cell. If the sheets oneither side of the insulator are extended beyond the edge of theinsulator as shown in FIG. 25, then the fiber layers can be connected toone another in series.

FIG. 26 is a cross-sectional view of a microcell bundle 350 comprisingan assembly of positive electrodes 354 interspersed with negativeelectrodes 352 in a bundled conformation.

FIG. 27 is a side elevation view of series-connected microcellsub-bundles 360 including sub-bundles 362, 366, 370 and 374interconnected by connectors 364, 368 and 372, respectively. Theconnectors are desirably highly flexible and most preferablyomnidirectionally flexible to accommodate accordion folding of the chainof sub-bundles, so that when folded back against a preceding sub-bundleor folded forwardly against the succeeding sub-bundle.

FIG. 28 is a perspective view of a connector 376 that may be used tojoin component microcell sub-bundles in series. The connector 376comprises a spaced-apart pair of crimpable leaves 378, 380, each ofwhich is crimpable by means of a pliers or similar tool, tocompressively grip a protruberant group of current collectors of asub-bundle. The leaves are electrically conductive, and are themselvesinterconnected by a flexible yoke element 382, which may comprise wireor metal filament, etc. that serves to electrically interconnect therespective sub-bundles with which leaves 378 and 380 are coupled.

FIG. 29 is a cross-sectional elevation view of a multibundle assembly390, wherein each bundle 391 has a corresponding feed tube 394associated therewith, and is mounted in a tubesheet 393 and leak-tightlysealed therein with an O-ring sealant element 392.

FIG. 30 is a cross-sectional elevation view of the multibundle assemblyof FIG. 29, wherein the respective bundles are connected in series andare numbered correspondingly to FIG. 29. The respective adjacent bundlesare interconnected by terminal elements 396 and 400 joined to oneanother by coupling wire 398 in series arrangement.

FIG. 31 is a cross-sectional view of a fuel cell module with multiplesub-bundles, numbered correspondingly to FIG. 29, and wherein blank sealelements 402 and 404 provide closure members for the tubesheet 393 ofthe module enclosure, when sub-bundles are removed.

FIG. 32 is a side view of a fuel cell module 410 with multiplesub-bundles 460, 462 and 464 of microcell elements, with a feed tube 450in a manifolded arrangement. The module includes a housing 422 enclosinga central interior volume 424 bounded by the housing wall of the moduleand by tubesheets 472, to which the sub-bundles are leak-tightly securedby means of O-ring elements 438, and 474, to which the sub-bundles areleak-tightly secured by means of O-ring elements 434.

The end sections of the housing enclose respective end volumes 426 and428. The end volume 426 contains a manifold to which the feed tube 450is joined in gas flow communication, for introduction of feed gas toeach of the three sub-bundles 460, 462 and 464 by means of the manifoldline 452 in communication with branch lines 454, 456 and 458 coupled tothe respective sub-bundles.

The sub-bundles are joined in series relationship to one another insequence, by connection line 440 interconnecting sub-bundles 460 and 462and connection line 442 interconnecting sub-bundles 462 and 464. Theexterior sub-bundles in such series are in turn joined respectively withterminals 444 and 446, as shown.

The right-hand end section of the housing is flangedly connected to themain central section of the housing by flange 430, with which mechanicalfastener means may be coupled to leak-tightly secure the componentsections of the housing to one another.

The housing is provided with a feed inlet 466 for introducing one of thefuel and oxidant streams into the end volume 426 for flow through thesub-bundles on the bore side thereof. An outlet 468 is joined to thehousing 422 at the left-hand section as shown, for discharge of spentfeed gas from the end volume of the housing.

The spent gas outlet 470 is provided in the main central section of thehousing, for discharge of spent feed from the shell side of thesub-bundle in the interior volume 424 of the housing.

FIG. 33 is a side elevation view in section, showing penetration of afeed tube 514 into the interior volume 506 of the housing 515 of amodule 480 containing microcell sub-bundles 494, 496, 489 and 498. Inthis arrangement, the sub-bundles are mounted in correspondingly sizedreceiving openings in tubesheets 500 and 502, leak-tightly secured inthe housing by means of O-ring sealing elements 492. In this way, theinternal volume of the housing is divided into a central volume 506 andend volumes 526 and 528.

The housing is provided with feed gas inlet 510, spent gas outlet 508and spent gas outlet 512. Spent gas on the shell side of the sub-bundleis discharged from the housing in outlet 508, and feed gas introduced ininlet 510 is flowed through the bore side of the sub-bundle anddischarged into end volume 528. From end volume 528 bore side spent gasis discharged from the housing in outlet 512.

The sub-bundles in the interior volume of housing 515 are joined inseries relationship to one another by means of series connector lines516, 518 and 520, and the outside sub-bundles in the series arrangementare in turn joined to terminals 522 and 524.

The housing 515 is openable at flange 443 to remove the right-hand endsection, following which the respective sub-bundles can be accessed forrepair or replacement.

Thus, microcell articles in accordance with the present invention may bereadily connected in series with one another, with successive adjacentarticles (fibrous microcell sheet layers, sub-bundles) being insulatedfrom each other by sheets or sheathing of porous insulating electricallynon-conductive material, or in other manner ensuring the absence ofelectrical interference between such adjacent microcell articles. Itwill be appreciated by those skilled in the art that the numbers ofsub-bundles shown in FIGS. 32 and 33, are illustrative only, and thatthe number of sub-bundles in a given application of the invention may bewidely varied depending on the energy generation requirements and otherstructural and operational parameters of the system in specificembodiments.

In the fabrication of high voltage electrochemical cells utilizingmicrocell articles of the invention, a bundle or sheet-form assembly ofmicrocells is fabricated. For example, if a design current of 200 ampsis required, a number of fibrous microcell articles are connected inparallel to generate the necessary current. The resultant microcellstructure then is either bundled in a cylindrical shape or used to forma multi-layered assembly. In a bundle, the positive and negative fibrouselements must be electrically insulated yet in intimate contact witheach other. To achieve higher voltages, the sheets or bundles areconnected in series, i.e., the positive of one cell is connected to thenegative of the next adjacent cell. The cells, bundles or sheetsconnected in series with one another are then potted and sealed in thesame housing to provide the desired high voltage electrochemical cellmodule.

Thermal Management

When microcell elements are bundled or otherwise aggregated in a compactstructural configuration to form modular electrochemical cellassemblies, the resulting electrochemical energy generation or energyconversion device generates significant heat in its operation.

Various methods can be utilized in accordance with the present inventionto remove heat from the microcell assembly.

In one aspect of the invention, heat exchange tubes are distributed inthe microcell bundles, sub-bundles, or other aggregated microcellassembly. In a preferred embodiment, such heat exchange tubes arealigned parallel with the fibrous microcell elements in the microcellassembly.

In another embodiment heat exchange tubes are placed between sub-bundlesin the assembly, so that the heat exchange tubes extend at least fromone end of a tubesheet face (in which the extremeties or outer portionsof the sub-bundles are mounted) to the opposite end. The number, size,and material of the heat exchange tubes are readily determined based onthe amount of heat that must be recovered, the fuel cell operatingtemperature, the type of heat exchange fluid used, and the pumpingrequirement or flow rate of the fluid, as will be appreciated by thoseskilled in the art.

In order to maintain separation of the heat exchange fluid from the feedthat is flowed to the bore side of the microcell fibers in the fuel cellmodule, the length of the heat exchange tubes can be selected such thatthe heat exchange tubes extend beyond the tube sheet that seals the boreside of the microcell hollow fibers from the shell side. The extendedheat exchange tubes then are potted again to form a barrier between thebore of the heat exchange tubes and the bore of the microcell hollowfibers.

The final assembly of the fuel cell module with the heat exchange tubespreferably includes the formation of a first housing with an inlet forthe introduction of heat exchange fluid in one end, a second housingbetween the two potted sections, i.e., the potted heat exchange tubesand the potted microcell elements, with an inlet for introduction offeed to the bore side of the microcell, and with the structure of thehousing being correspondingly constructed at the opposite end, toprovide corresponding respective outlets for discharge of the heatexchange fluid and the spent feed.

An alternative thermal management design for microcell electrochemicalcell modules according to the present invention employs hollow,nonporous, electrically and thermally conductive tubes, as currentcollectors for either the bore side or the shell side or both the shelland bore side of the microcell structures. Since the current collectorsterminate at opposite ends of each tube sheet, the heat exchange currentcollector tube will be potted as described hereinabove, to separate theheat exchange fluid housing from the bore side/feed only at one end. Atthe opposite end the heat exchange tube is terminated at the tube sheet.

This arrangement allows the heat exchange fluid and feed to the bore tobe mixed at the outlet. In this system design the heat exchange fluiddoes not enter the bore of the microcell to contact the catalyst or theelectrolyte. For example, the feed to the bore and the heat exchangefluid can be supplied to the module in the same direction, such that theheat exchange fluid and the feed to the bore can only mix at the feedoutlet from the microcells.

The heat exchange fluid then is recovered in a separate unit, or aplenum in the housing can be provided to collect the heat exchange fluidfor recycle. The separation of heat exchange fluid from the feed can bereadily achieved, e.g., in the case where the feed is air or hydrogengas.

In a specific embodiment, where the heat exchange fluid and the feed tothe bore are the same (for example, air), the heat exchange fluid andthe feed can be allowed to mix without further separation requirement.

In a further embodiment, heat is removed from the microcell module byconduction of heat from the current collectors on the shell side or boreside of the microcell elements. In this approach, the ends of thecurrent collectors are extended and immersed in a heat exchange fluid ina plenum inside the housing containing the microcell module or in a heatexchange passage located within the housing, at the feed inlet to oroutlet from the fiber bores. In the latter case, the inlet and outlet ofthe heat exchange passage are leak-tightly segregated from the interiorvolume of the microcell module.

Referring to the drawings, FIG. 34 is a cross-sectional view of amicrocell assembly 530 in which heat exchange fibers or tubes 538 areprovided in interspersed (distributed) relationship to the microcellbundles 532, as shown.

In the illustrated microcell assembly, each microcell bundle is mountedin a correspondingly sized opening in a tubesheet 536, with themicrocell bundle being leak-tightly sealed in such opening by means ofan O-ring sealing element. Alternatively, the microcell bundles 532 andheat exchange tubes 538 are potted to form tube sheet 536.

FIG. 35 is a sectional elevation view of a fuel cell module, showingair/fuel passages and heat exchange passages thereof.

The fuel cell module 540 comprises a housing 541 in which a microcellassembly 550 is mounted, by means of potting members 552 and 554, whichare circumferentially sealingly engaged with the inner wall of thehousing by means of O-ring sealing elements 556 and 558. In this manner,there is formed an interior volume 560 in the housing, bounded by thepotting members 552 and 554. A gas discharge outlet 586 is provided inthe main central portion of the housing, in gas flow communication withthe shell side of the microcell elements in the assembly 550.

The fuel cell module of FIG. 35 also features respective tubesheets 562,sealingly engaged with the inner wall of the housing 541 by means ofO-ring sealing element, and tubesheet 578, sealingly engaged with theinner wall of the housing by means of O-ring sealing element 580.

By such arrangement, an intermediate volume 576 is provided between thepotting 552 and tubesheet 578, and an end volume is provided at theextremity of the housing, in the left-hand portion in the view shown.

Correspondingly, an intermediate volume 568 is formed between thepotting member 554 and the tubesheet 562, as well as an end volume atthe right-hand end portion of the housing in the view shown in FIG. 35.

Coolant inlet 582 is provided at the right-hand end volume portion ofthe fuel cell module housing, and a coolant outlet 590 is provided atthe left-hand end portion of such housing.

A feed inlet 584 is provided in communication with the intermediatevolume 568 of the module and a spent feed outlet 588 is provided in flowcommunication with the intermediate volume 576 at the opposite end ofthe module.

Distributed across (transverse to the longitudinal axis) cross-sectionof the microcell assembly 550 is a plurality of hollow fiber heatexchange passages 604, which extend through the entire length of themicrocell assembly and intermediate volumes through the tubesheets 562and 578 into the end volumes 566 and 565, respectively.

A central feed tube 592 enters the vessel from the right-hand sidethereof and extends centrally into the microcell assembly 550. Withinthe microcell assembly, the feed tube is of a perforate character, toprovide feed to the shell side of the fibrous microcell elements in themicrocell assembly.

Current collector elements in the respective intermediate volumes 568and 576 engage respective terminals 600 and 602, which extend exteriorlyof the housing 541.

The housing 541 is provided with a flange 570 connection, secured bysuitable mechanical fasteners, whereby the right-hand intermediatevolume and end volume portion of the housing is removable to access theinterior elements of the fuel cell module.

In operation, the coolant medium (from an external source, not shown inFIG. 35) is flowed into the end volume 566 and passes through theopen-ended heat exchange tubes 604 and flows axially through such tubesto the opposite end volume 565, from which the coolant is dischargedthrough outlet 590, and may for example be subjected to heat recoveryfor re-circulation of coolant to the inlet 582 in a continuous loopfashion. Concurrently, feed (oxidant and fuel) are introduced torespective shell side and bore side of microcell elements in themicrocell assembly 550 to effect electrochemical reaction generatingpower transmitted to an external load through the respective terminals600 and 602, which are joined to appropriate circuitry and external loadcomponentry, for such purpose.

FIG. 36 is a cross-sectional view of a microcell bundle 610incorporating hollow fibers 614 interspersed with fibrous microcellelements 612. In such bundle, the hollow fibers function as outerelectrode elements, as well as enabling heat exchange. Accordingly, thehollow fibers may be coated, impregnated or extruded withelectrocatalyst material or otherwise configured for functional use aselectrode elements, in addition to providing a throughbore passage inthe lumen thereof, for flow of a heat transfer medium, e.g., air, therethrough, to effect heat removal from the bundle, incident toelectrochemical reaction heat generation in the operation of themicrocell assembly.

FIG. 37 is a side elevation in section of a fuel cell module utilizinghollow fiber heat exchange elements.

The fuel cell module 620 of FIG. 37 comprises a housing 625, which isflanged with flange structure 624, to allow separation of the right-handportion of the housing to be removed from the main central portion, toaccess internal structures of the module. The housing 625 contains amicrocell bundle 626 which is potted by potting numbers 628 and 630, andleak-tightly sealed against the interior wall surface of the housing625, by O-ring sealing elements 632 and 634, to define an interiorvolume 636 within the housing bounded by the interior walls andrespective potting members 628 and 630.

In axially spaced relationship to the potting number 630 is a tubesheet640, thereby defining an intermediate volume 660, which is sealed byO-ring element 642 against the interior wall of the housing.

The heat exchange tubes constituting current collectors, terminate attube sheet 628, with heat exchange/current collector tubes communicatingwith end volume 662 of housing 622.

Exterior of the tubesheet 640 within the housing is an end volume 658.

A central feed tube 641 extends through the end-wall 622 of the housingand is centrally extended in to the microcell assembly 626. Such centralfeed tube is perforate within the microcell assembly, to provide fuel tothe shell side of the assembly.

The right-hand portion of the housing is removable at flange 624 toprovide access to the interior elements of the module.

The intermediate volume 660 is provided with an inlet 646 forintroduction of fuel thereto for flow through assembly 626 to volume662, the latter being provided with outlet 648 for discharge of spentfuel therefrom.

The intermediate volume 636 of the housing is provided with outlet 638for discharge of shell side spent feed.

The end volume 658 of the module is provided with inlet 644 forintroduction of coolant for flow through hollow fiber elements extendingin to such volume, for axial flow through the hollow fiber electrodeelements to the opposite end volume 662.

The hollow fiber heat exchange passages in this embodiment are formed byhollow fiber electrodes, and such electrodes are coupled in therespective end volumes to the corresponding terminals 652 and 656, asillustrated.

FIG. 38 is a sectional elevation view of a fuel cell module with heatexchange from current collectors by means of conduction. The module 700includes a housing 702 containing microcell assembly 704, potted byrespective potting numbers 706, sealed by O-ring sealing element 710,and potting number 708, sealed by O-ring sealing element 712. Aninterior volume 720 is thereby defined, communicating with the outlet740 for discharge of spent feed from the interior volume 720.

A central feed tube 714 extends centrally in to the microcell assembly704 and is perforate over its length within the microcell assembly, toprovide feed to the shell side of the assembly.

The end volume 724 of the housing 702 is provided with an inlet 742 forintroduction of feed for flow through bore passages of the microcellassembly 704 to the end volume 722 from which spent feed can bedischarged from outlets 732.

In this module, a heat exchanger 746 is contained in end volume 724 andjoined in heat exchange contact with current collector elements of themicrocell assembly. A heat exchange fluid (from a source not shown inFIG. 38) is introduced to heat exchange or inlet 748 and circulatedthere through for discharge from outlet 750.

In like manner, the opposite end volume 722 contains a heat exchanger780 with an inlet 728 receiving heat exchange fluid for flow therethrough and discharge from the second heat exchanger 780 through outlet730.

The current collector elements at respective ends are joined inelectrically conductive relationship to terminals 738 and 736. Theleft-hand portion of the housing 702 is flanged by flange 726, wherebythe housing can be readily opened to access internal elements of thehousing.

FIG. 39 is a schematic representation of a fuel cell system, accordingto one embodiment of the invention.

The fuel cell system 780 includes a microcell module 782, which includesa housing 784 having joined thereto a coolant medium inlet 810, acoolant medium outlet 792, a fuel inlet 794, an oxidant inlet 799, aspent fuel outlet 786 and a spent oxidant outlet 804. The feed outlet786 is joined to a discharge line containing back pressure regulatingvalve 788 therein. In like manner, the spent oxidant outlet 804 isjoined to discharge line 806 containing back pressure regulating valve808 therein. The respective back pressure regulating valve 788 and 808may be modulated to control the rate and extent of electrochemicalreaction involving the fuel and oxidant species.

The system includes fuel supply tank 798 joined by fuel feed line 796 tothe feed inlet tube 794. Correspondingly, an oxidant tank 802 isprovided, joined to oxidant feed line 800 coupled to oxidant inlet 799.

The system involves a coolant recirculation arrangement, includingrecirculation line 816 joined to coolant outlet 792 and having disposetherein a pump 818 and heat exchanger 820. Heat exchanger 820 effectsheat removal from the warmed coolant medium, so that same is recycled tothe surge tank 814 for return in feed line 812 to coolant inlet 810.

Accordingly, an operation of the system shown in FIG. 39, the coolantmedium is flowed through hollow fiber heat exchange tubes in the housingand is continuously recirculated to the surge tank to provide a hold-upinventory of coolant for high rate electrochemical oxidation.

Double Membrane Microcell Structures and Assemblies

Microcell structures are usefully employed in specific applications ofthe invention in a double membrane configuration.

In one embodiment, microcell structures of such type are readily formedusing an inner hollow fiber separator having an inner current collectorand electrocatalyst of the inner electrode on its shell side. Such innerhollow fiber separator is encapsulated by an outer hollow fibermembrane. The pores of the outer hollow fiber membrane are impregnatedwith an electrolyte and the electrocatalyst of the outer electrode iscoated on the shell side of the outer hollow fiber membrane, to form adouble membrane microcell structure.

This double membrane microcell structure is advantageous to enable theinner hollow fiber separator to be used as a membrane to selectivelyallow permeation of feed (e.g., hydrogen or oxygen), as desired. Thismay be effected, for example, by coating the inner wall or the outershell of the inner separator with a perm-selective material thatpreferentially allows the desired gas to permeate to the electrode. Thisdouble membrane design thus is advantageous in reducing or eliminatingthe exposure of the electrocatalyst or the electrolyte to potentialpoisonous impurities in the feed. Materials that may be used in theperm-selective membrane include cellulose esters, polyimides,polysulfones and palladium.

In another microcell structure including a double membrane separator,the inner wall of the inner separator may be impregnated or coated witha CO—H₂O shift low temperature reforming catalyst. In such design, theshell side of the inner separator is coated with an anode or cathodefeed-selective material.

Another double membrane design involves coating both anode and cathodewith a hydrogen- or oxygen-selective material. In such instance, theprotective perm-selective material on the shell side of the outer hollowfiber membrane must be electrically conductive to allow electricalcontact between the current collector of the outer electrode and theelectrocatalyst on the shell side. A perm-selective material such aspalladium can be used for such purpose. Alternatively, an electricallyconductive perm-selective material can be applied only to one of thecathode and anode components, if desired.

Yet another design utilizing double membrane fabrication employs anelectrically conductive inner hollow fiber separator. Such electricallyconductive hollow fiber separator may be formed of sintered metal,carbon or graphite. In some embodiments of such double membrane design,an inner current collector may not be needed depending on the electricalconductivity of the inner hollow fiber.

The inner and outer hollow fiber membrane can be of any suitablecommercially available membrane material, including, for example,polypropylene, polysulfones, polyacrylonitrile, etc. In one embodiment,the membrane is treated to impart perm-selective characteristics, e.g.,to selectively allow permeation of the feed gases (fuel, oxidant) whileremaining impermeable to other gases and components (such as fuelimpurities) that may be present. By way of specific example, aprotective hydrogen-permeable barrier layer can be deposited by solutiondeposition, electrolytic coating, etc., to provide a film of palladiumon the membrane surface that allows passage of hydrogen therethrough,but occludes nitrogen and oxygen. See, for example, Gryaznov et al.,“Selectivity in Catalysis by Hydrogen-Porous Membranes,” Discussions ofthe Faraday Society, No. 72 (1982), pp. 73-78; Gryaznov, “HydrogenPermeable Palladium Membrane Catalysts,” Platinum Metals Review, 1986,30 (2), pp. 68-72; and Armor, “Catalysis with Permselective InorganicMembranes,” Applied Catalysis, 49 (1989), pp. 1-25.

FIG. 40 is a cross-sectional view of a double membrane design of amicrocell 900 with an electrically conductive perm-selective membrane onthe anode or cathode element of the microcell. The microcell 900comprises an outer electrocatalyst layer 912, the microporousmembrane/electrolyte matrix 910, electrocatalyst 908, an inner hydrogen-or oxygen-selective membrane 906, and current collector or electrodeelements 902 in the inner bore 904.

FIG. 41 is a cross-sectional view of a double separator design of amicrocell 914 with perm-selective membranes protecting the anode orcathode elements of the microcell. The microcell 914 comprises an outerelectrocatalyst layer 930, the microporous membrane/electrolyte matrix928, electrocatalyst 926, current collector or electrode elements 922,inner porous separator 920, an inner hydrogen- or oxygen-selectivemembrane 918 and an inner bore 916.

FIG. 42 is a cross-sectional view of a double separator design of amicrocell 932 with perm-selective membranes covering both anode andcathode elements of the microcell. The microcell 932 comprises an outerhydrogen- or oxygen-selective electrically conductive membrane 948,electrocatalyst layer 946, the microporous membrane/electrolyte matrix944 electrocatalyst 942, current collector or electrode element 940,inner porous separator 938, an inner hydrogen- or oxygen-selectivemembrane 936 and an inner bore 934.

FIG. 43 is a cross-sectional view of a double separator design of amicrocell 950 with perm-selective membranes covering both anode andcathode elements of the microcell and with an electrically conductiveinner separator. The microcell 950 comprises an outer hydrogen- oroxygen-selective electrically conductive membrane 966, electrocatalystlayer 964, the microporous membrane/electrolyte matrix 962,electrocatalyst 960, electrically conductive porous current collector orelectrode element 958, an inner hydrogen- or oxygen-selective membrane956 and an inner bore 952.

FIG. 44 is a cross-sectional view of a double separator design of amicrocell 970 with perm-selective membranes covering both anode andcathode elements of the microcell and with reformer catalyst on theinner wall of the inner separator. The microcell 970 comprises an outerelectrocatalyst layer 986, the microporous membrane/electrolyte matrix984, electrocatalyst 982, current collector or electrode elements 980,an inner hydrogen- or oxygen-selective membrane 978, inner porousseparator 976, CO water shift/reforming catalyst 974, and an inner bore972.

Manufacture of Microcell Structures and Assemblies Comprising Same

For commercial high-volume production, the microcell device with most ofits components desirably is fabricated in a single extrusion step, athigh rate. A critical aspect of the high-volume fabrication process isencapsulating the inner electrode with the microporous membraneseparator.

For such purpose, a strand or tow of electrically conductive fibers canbe passed through the center of the bore former tube of an extrusionmold (spinnerette). The material that will form the backbone of themicroporous membrane separator, referred to as a “dope,” is extrudedaround the bore former tube in continuous fashion onto the strand or towof electrically conductive fiber(s). An internal coagulant fluid, e.g.,a gas such as nitrogen or a liquid such as water, is passed through thebore former tube along with the inner electrode fiber(s) or fibrouscurrent collector(s).

In the above-described operation, the size of the microcell fiber isdetermined by the size of the orifice of the extrusion mold. Suchorifice can be widely varied in size, e.g., from as small as 100 micronsor smaller, with the membrane correspondingly being as thin as a fewmicrons in thickness.

An electrocatalyst paste is simultaneously extruded through the bore ifthe method of microcell fabrication utilizes an ink paste. Extrudedfiber is immersed in a quenching bath or an external coagulant medium,such as water. As the extruded fiber passes through thecoagulation/quench operation, the microporous membrane structure isinstantaneously formed around the inner electrode as the water-solublepore former compound is leached out in the coagulant/quenching medium.

Pore structure, porosity and pore size of the membrane separator therebyare accurately controlled by selection and corresponding control ofparameters such as the membrane dope formulation, type of coagulantused, temperature of the spinning operation, etc. Specific conditionsare readily determinable for such process by simple experiment withoutundue effort, by those skilled in the art.

A wide variety of materials are useful to form the microporous membraneseparator, including, without limitation, polysulfone,polyacrylonitrile, other high temperature polymers, glass and ceramicmaterials.

By the above-described spinning process, microcell articles can befabricated at high rate on a continuous basis.

After formation of the microporous membrane separator-encapsulated innerelectrode structure, such encapsulated structure is coated orimpregnated on the outside (shell side) with an ion exchange polymer inthe case of polymer electrolyte fuel cells, and/or electrocatalyst ofthe outer electrode. Such exterior coating can be advantageouslyperformed by a similar extrusion process.

FIG. 45 is a schematic flowsheet of a solution impregnation system 988for impregnation of a membrane fiber 992 with Nafion or electrocatalyst.The membrane fiber 992 is dispensed from a fiber spool 990 and passes,by action of the roller 994, through a solution bath 996 in which thefiber is impregnated. The impregnated fiber then passes over guide roll998 and through the bank of heating elements 999 for final collection ontake up winder 1000.

Additional applications for electrochemical cells of the inventioninclude production of chemicals. Chemical synthesis applications areadvantageously effected utilizing microcells fabricated in accordancewith the invention, which provide: high current density per unit volume,as necessary for chemical synthesis; low internal resistance due tominimal electrode membrane distance (thickness); and high efficiency dueto low mass transfer resistance.

In addition, microcells fabricated in accordance with the presentinvention may be utilized to generate hydrogen and oxygen where otherforms of electric power are available. In such applications, hydrogen(or other fuel gas) generated by the cell can be stored and used forgeneration of electricity.

For example, after the porous polymeric membrane has been formed aroundcurrent collector(s) of a microcell fiber structure, the structure canbe directly passed through a solution of aqueous polymeric electrolyte,such as a solution of Nafion (5% solids in water and alcohol) polymericelectrolyte, to impregnate the pores of the porous polymeric membranewith the polymeric electrolyte. The amount of the impregnated polymericelectrolyte may be selectively varied depending on the residence time ofthe porous polymeric membrane in the electrolyte impregnant composition,and the number of times that the structure is repetitively exposed tothe composition (i.e., in single-pass or multi-pass fashion) duringprocessing.

On the same process line in which the electrolyte is impregnated, oralternatively in a subsequent phase of the fabrication operation, themicrocell fibers in one process embodiment are dried and impregnatedwith platinum as the electrocatalyst material, using a plating solutioncontaining H₂[PtCl₆], following which the fibers are passed through abath of reducing agent, such as sodium borohydride (NaBH₄), to reducethe platinum composition to elemental platinum metal.

This continuous technique according to one embodiment of the inventionis used to impregnate only the outer shell of the membrane withplatinum. The inner wall of the membrane is impregnated after the fibershave been potted in the vessel by pumping the platinum plating solutionthrough the bore of the fibers.

In another embodiment, both the shell and the bore side of the fibersare impregnated after the fibers have been potted.

After the ion exchange Nafion electrolyte solution is impregnated in thepores of the membrane, the electrocatalyst is coated according toanother aspect of the invention by using platinum loaded on activatedcarbon of suitable particle size. The platinum loading on the activatedcarbon particles typically is in the range of from about 5 to about 10percent by weight. A paste is prepared consisting essentially ofplatinum loaded activated carbon, Nafion ionomer as the binder, and aTeflon® polytetrafluoroethylene emulsion. The paste then is coated, oralternatively extruded, on the shell side of the fibers.

Coating of the paste inside the fiber wall may be accomplished invarious ways. In one approach, the paste is coextruded while the porousmembrane separator element is being spun around the current collector. Asecond approach is to pre-extrude the paste around the current collectorbefore inserting the current collector into the membrane fiber. As athird approach, a thin paste can be pumped into the bore of the porousmembrane separator element after the cell assembly and potting has beencompleted.

In another embodiment, the electrolyte is deposited inside the porousmembrane separator element, and the catalyst is applied byelectrodeposition from a solution containing platinum ions, by anelectrolytic plating solution process, or by an electroless platingsolution process.

Corrosion Management in the Microcell Assembly

In applications of conventional fuel cell technology, current collectorsgenerally have been limited to the use of graphite type materials.Current collectors formed of aluminum or titanium can be coated withcorrosion-resistant coatings such as gold, but such coatings tend topeel and delaminate from the current collector element under the severecorrosive conditions and thermal cycles that characterize the fuel celloperation.

The use of microcell elements permits current collector materials ofconstruction other than graphitic materials to be employed. Metal fibersutilized in microcell structures in the electrochemical cell module canbe coated by variety of techniques to achieve durable corrosionresistance. Useful coating techniques for such purpose include, withoutlimitation, electrochemical deposition, electroless coating, dipcoating,extrusion, etc., using corrosion resistant metal compositions orpolymeric materials such as polyanaline.

A preferred approach for coating metal substrates for use as currentcollector involves use of amorphous metal compositions deposited byplasma coating techniques. In general, better corrosion resistance isattributable to the amorphous nature of the coating structure. Further,various amorphous metal compositions generate extremely high surfaceareas. Examples of such high surface area metal compositions includenickel metal hydride electrocatalyst materials. The use of such highsurface metal compositions coupled with the inherently high surface areaof the fibrous geometry of the microcells enables such amorphous metalcoatings to be effectively utilized for hydrogen storage capability inthe fuel cell, a potentially significant structural and operationaladvantage.

As another approach to increase the corrosion resistance of metallicfiber substrates, the metal fibers can be coated with a polymericprecursor or other organic coating, and the coating then is carbonized.Carbonization of the polymer to form graphitic material on metallicfibers yields a coating that is corrosion resistant, yet possesseselectrical conductivity that is higher than that of carbon or graphitealone.

The presence of pinholes in any coating application can cause corrosionand electrical disconnection of one section of the microcell fromothers, which in turn reduces the useful power density of the cell. Inanother approach, such electrical disconnection deficiencies are avoidedby a fabrication method involving co-placement of a carbon fiber in thebore or on the shell side of the microcell, so that the carbon fiber isin intimate contact with the associated current collector of themicrocell. With such arrangement, if the current collector iscorrosively attacked in the operation of the electrochemical cell, thecarbon or graphitic fiber then continues to maintain a flow of currenttherethrough, thereby providing electrical continuity despite even grosscorrosion-mediated breakage or deterioration of the current collectorelement.

To enhance the service life of metallic current collector fibers in thecorrosive environment of a fuel cell, the metal fiber is advantageouslycoated with a compound such as a polymeric material, following which thecoated fiber is subjected to pyrolysis conditions for the polymericmaterial. The fiber coating material is pyrolyzed and converted tocarbon using techniques that are conventionally employed to form carbonfibers per se.

Formation of a continuous layer of carbon on a metallic currentcollector fiber (of any size) produces a fiber that is electricallyconductive radially and longitudinally and at the same time iscorrosion-resistant due to the surface layer protecting the underlyingmetal from corrosive attack.

FIG. 46 is an elevation view of a conductor element 1002 including ametallic fiber 1004 having a polymeric compound coating 1006 on itsouter surface. The fiber is coated in any suitable manner, e.g., byspraying, dip-coating, roller coating, etc.

FIG. 47 shows the corresponding fiber 1002 of FIG. 46 after thepyrolysis step, as comprising a pyrolyzed carbon coating 1008 on theoutside surface thereof.

Concerning current collector and electrode preparation, the electricallyconductive metal fibers of the microcell in one embodiment of theinvention comprise copper, aluminum or titanium fibers, having adiameter in the range of from about 100 to about 10,000 microns, coatedwith a suitable thickness of corrosion-resistant material such as goldor platinum.

Alternatively, carbon/graphite fibers having diameter in the range offrom about 100 to about 10,000 microns and having good electricalconductivity characteristics can be employed, and metallized with theelectrocatalyst, e.g., platinum. Such platinum metallization isadvantageously effected by contacting the fibers with a plating solutioncontaining H₂[PtCl₆], followed by reduction of the platinum compound toelemental platinum metal via contact with sodium borohydride (NaBH₄).

With respect to current collectors, the presence of pinholes or coatingdefects causes accelerated corrosion of metallic current collectors. Inconsequence of such corrosion, the fiber cell can disconnect (as aresult of the continuity of the conductor being impaired) and becomeinoperable. To avoid this disconnection of part of the microcell voltageand current, fibrous carbon current collectors advantageously are laidalong the coated metallic fibers. FIG. 48 shows a conductor 1010including a fibrous carbon current collector 1014 laid along a coatedmetallic fiber 1012. The carbon fiber 1014 will be in intimate contactwith the coated fiber 1012, as shown in FIG. 48.

FIG. 49 shows the fiber assembly of FIG. 48 after a disconnection breakof the coated metallic fiber 1012. In the event of a corrosion pointbreak in continuity of the coated metallic fiber, the carbon fiber 1014in contact with both sections of the corroded metal fiber 1012 providescontinuity enabling the current to pass from one side to the other alongthe length of the carbon fiber/metallic fiber arrangement.

Water Management in Microcell Assemblies

In microcell electrochemical reactions wherein water is a reactionby-product, a feed may be humidified to prevent drying of the membrane,the microcell assembly desirably includes a water management system foraddition and removal of excess water from the microcell assembly.

In general, the high surface area of microcell structures, and lowermass transfer resistance, mean that the removal of water from themicrocell module is less problematic than in conventional planar fuelcell structures.

Various alternatives can be employed to further enhance the watermanagement capacity of the microcell fuel cell module. For example, ifheat exchange tubes are employed in the fuel cell assembly, comprisinghollow fiber membranes coated with Nafion or other ion-exchange polymeror material that will selectively allow water permeation, and if theheat exchange liquid is water, the heat exchange tubes can be used forwater supply to the fuel cell and removal of heat from the fuel cell.

One approach for water removal from the fuel cell is to provide porousplane hollow fiber membranes in the microcell bundle, in distributedfashion therein. In this structural arrangement, water will permeatethrough the membrane wall by a wicking action during operation of thefuel cell and will be channeled down the bore of the hollow fiber andaway from the active surfaces. The resultingly channeled water then canbe collected in a plenum provided in the housing containing the module,for discharge from the system.

Concerning the removal of water from fuel cells, various approaches arecontemplated by the present invention. To remove water produced in thefuel cell made from fiber cells or microcells, hollow fiber membranestreated with a hydrophilic compound can be packed intermittently withfiber cells containing an electrode or current collector. Since thesehollow fiber membranes are in intimate contact with the shell side ofthe cells and are open on the bore side, water produced in the fuel cellis absorbed by a wicking action and channeled down the bore of themembrane hollow fiber membrane away from the cells containing theelectrode, thereby eliminating the water flooding in the cell.

If the module is mounted vertically, then water may be collected bygravity collection at the bottom of the cell and discharged therefrom.

FIG. 50 shows a cross-section of a hollow fiber and microcell tubebundle 1020, in which the plane hollow fiber elements 1026 areinterspersed with the microcell fiber elements 1022 and shell sideelectrodes 1024, and such hollow fiber elements are used for channelingwater from the assembly.

FIG. 51 is a sectional elevation view of a microcell fuel cell module1030, including a housing 1032 containing a microcell assembly 1036arranged vertically as shown. The housing 1032 has a flange 1034 bymeans of which the upper end of the housing can be removed to access themicrocell assembly and other internal components of the module.

The microcell assembly 1036 is potted at its upper end by potting member1040 leak-tightly sealed to the inner wall of the housing by O-ringsealing element 1042. In like manner, the microcell assembly 1036 ispotted at its lower end by potting member 1044 leak-tightly sealed tothe inner wall of the housing by O-ring sealing element 1046.

The microcell assembly 1036 engages a central feed tube 1080, which isperforate within the interior volume of the microcell assembly.Additionally, feed inlet 1060 provides feed to the bore side of themicrocell elements in the assembly, from upper end volume 1048. Feeddischarged at the lower end from the hollow fiber elements enters thelower end volume 1050 and is discharged from the housing from outlet1072 or outlet 1070.

Outlet 1078 is provided for interior volume 1038 of the housing, fordischarge of spent feed from the interior volume (shell side).

The lower end of housing 1032 constitutes a plenum chamber 1076 whichreceives access water (condensate) gravitationally flowed to such lowerend of the housing, and discharged by overflow through outlet 1072 oroutlet 1070.

The current collector elements at respective ends of the microcellassembly are joined to respective terminals 1082 and 1084, asillustrated.

Accordingly, the hollow fiber tubular elements employed in the microcellassembly allow permeation of excess water in to the bore passages ofsuch hollow fibers and drainage thereof to the plenum chamber, toreadily remove excess water from the electrochemical fuel cell module.

Any other suitable means or methods can be used to channel water fromthe microcell assembly, including elements or structures that utilizesurface tension or capillarity effects to induce channelized flow ofwater from the microcell bundle to a collection vessel or locus. By wayof example, the enhancement structure for film condensation apparatusthat is described in U.S. Pat. No. 4,253,519 issued Mar. 3, 1981 toLeslie C. Kun and Elias G. Ragi is usefully employed as an overlaystructure on the microcell fibers or bundles or sub-bundles comprisingsame, to effect channelized flow of liquid for recovery and dischargethereof from the fuel cell module.

In each of the foregoing approaches, theelectrolyte/catalyst-impregnated coated fiber can be optionally coatedwith a Teflon® polytetrafluoroethylene emulsion, to imparthydrophobicity to the membrane/electrode assembly. By such expedient,water introduced or formed in the cell will be repelled from thecatalyst surface, to enhance the availability of the catalyst site tothe fuel or the oxidant (e.g., hydrogen, or oxygen).

While the invention has been described herein with reference to specificembodiments, features and aspects, it will be recognized that theinvention is not thus limited, but rather extends in utility to othermodifications, variations, applications, and embodiments, andaccordingly all such other modifications, variations, applications, andembodiments are to be regarded as being within the spirit and scope ofthe invention.

What is claimed is:
 1. An electrochemical device comprisingwater-permeable membrane hollow fibers distributed in an assemblyincluding a plurality of microcells potted at respective ends of theassembly and disposed within a housing wherein the potted respectiveends bound an interior volume therebetween, and wherein the hollowfibers are parallelly aligned with microcells of the assembly, with eachhollow fiber having a first open end extending through the tubesheetexteriorly of the interior volume and the other end terminating at orbefore the opposite potting member, whereby the hollow fibers arearranged to absorb water produced in the electrochemical reaction bywicking action and channeling water away from the locus ofelectrochemical reaction by permeation through the wall of the hollowfiber and flow thereof through the bore of the hollow fiber to acollection locus in the housing outside of the interior volume.
 2. Anelectrochemical device according to claim 1, wherein the housing isoriented so that the microcell elements and the hollow fibers arevertically aligned, whereby the collection locus in the housing is atthe lower end of the housing, and water in the bore of the hollow fiberflows gravitationally downwardly to the collection locus.
 3. Anelectrochemical device according to claim 1, wherein each hollow fiberis coated on its exterior surface with a hydrophilicity-imparting agent.4. An electrochemical device according to claim 1, wherein each hollowfiber is formed of a material selected from the group consisting ofpolymeric materials, glasses and ceramics.
 5. An electrochemical deviceaccording to claim 1, wherein the hollow fiber has a porosity in a rangesuitable for application selected from the group consisting ofultrafiltration, microfiltration and reverse osmosis.
 6. Anelectrochemical device according to claim 1, wherein the hollow fiberhas an outer diameter in the range of from about 100 micrometers toabout 10 millimeters.
 7. An electrochemical device according to claim 1,wherein each hollow fiber is formed of a hydrophilic material.
 8. Amethod of water management in an electrochemical device including aplurality of microcells potted at respective ends and disposed within ahousing wherein the potted respective ends bound an interior volumetherebetween, said method comprising arranging hollow fibers to absorbwater produced in the electrochemical reaction by wicking action,channeling water away from the locus of electrochemical reaction bypermeation through the wall of the hollow fiber and flowing same throughthe bore of the hollow fiber to a collection locus in the housingoutside of the interior volume.
 9. A method according to claim 8,wherein the microcell elements and the hollow fibers are verticallyaligned, whereby the collection locus in the housing is at the lower endof the housing, and water in the bore of the hollow fiber flowsgravitationally downwardly to the collection locus.
 10. A methodaccording to claim 8, wherein each hollow fiber is coated on itsexterior surface with a hydrophilicity-imparting agent.
 11. A methodaccording to claim 8, wherein each hollow fiber is formed of a materialselected from the group consisting of polymeric materials, glasses andceramics.
 12. A method according to claim 8, wherein the hollow fiberhas a porosity in a range suitable for application selected from thegroup consisting of ultrafiltration, microfiltration and reverseosmosis.
 13. A method according to claim 8, wherein the hollow fiber hasan outer diameter in the range of from about 100 micrometers to about 10millimeters.
 14. A method according to claim 8, wherein each hollowfiber is formed of a hydrophilic material.